Using KNACRO 4-Channel 16Bit ADC with PGA for RPI Raspberry PI 16 Bits I2C ADS1115 Module ADC 4 Channel for Raspberry Pi 3/2 Model B/B+ under 2.7 simpletest.py worked. Changed to SeeedStudio 4-Channel 16-Bit ADC for Raspberry Pi (ADS1115) and get same resource not found under 2.7. At least with Knacro I could easily switch address. With SeeedStrudio, it seem a need to unsolder one bridge and solder another. Pretty stupid.

Maybe check for any overlays that have been activated in /boot/config.txt? Not sure why the kernel would bind to the ADS on the I2C bus without some prior doing. The basic library shouldn't cause that behavior.

Here's an ADS1115 breakout on a Pi 0 W with Raspbian Lite. It sees the ADS as expected: